Washers are stamped out in a metal press at high speed and in very numerous quanties at a time. The metal used is flat, the thickness of the washer, but the metal is usually recycled, junk, with all kinds of different metals of varried hardnesses. Sooooo, when a washer is put onto the arrow, it can and does have heavy sides and lighten sides, and ununiformed thickness,thereby turning the washer is like putting wheel weights on your tires at the lighter side of the wheel to compinsate. It balances the arrow and also puts a different thickness of the washer on a different part of the arrow and, wallio, a better spinning arrow. Easy, peasy, Japaneasy.
BBO